1. Field of the Invention
The present invention relates to a method to identify whether a cell is cancerous or normal.
2. Description of the Related Art
Humans are still far from conquering cancer. Traditional biochemical methods seem to run out of steam. There is a hope that the achievements of modern nanotechnology, physical sciences may bring novel alternative methods to attack on cancer. The challenges for scientists working in the area of cancer are often multidisciplinary in nature. Recent advances in this field are a result of inter-disciplinary research involving physics, chemistry, molecular biology, engineering and medicine. Research efforts over the years have resulted in the development of DNA chips, miniaturized biosensors and bioMEMS. These smart microsystems have found applications in gene expression profiling, drug delivery and clinical diagnostics. In particular, the development of highly sensitive probes for detection of cancer has attracted considerable attention in biology and medical research fields.
As an example, cervical cancer is the second leading cancer in women worldwide and infection with high risk human papillomavirus (“HPV”) is the most significant risk factor in its etiology. HPV causes a common sexually transmitted infection among both women and men. The objective of screening for cervical cancer is to prevent persistent HPV infection and death by detecting and treating high-grade squamous intraepithelial lesions, which are precursor lesions for invasive cancer. A simple and effective screening method is of prime and utmost importance especially in many developing countries where cervical cancer rates are particularly high. In the United States, an estimated 12,900 cases of cervical cancer and 4,400 deaths occur annually.
The Papanicolaou (“Pap”) smear test has proven to one of the most successful methods of cancer detection over the years. Although the Pap test is the most widely used cancer screening method in the world and its impact in the incidence of cervical cancer is well known from a historical perspective, recent reports suggest that the sensitivity of Pap smear is 50-60%, with the relative proportion of sampling to screening errors being 2:1. The tests may be further complicated by high unsatisfactory rates, preparation artifacts and unnecessary cost interventions. Each year in the United States alone approximately 3.6 million cell pathology tests are classified equivocal, out of which only 8% of women have precancerous (high-grade squamous intraepithelial) lesions, and 0.4% have cancer. The economic constraints in developing countries have prompted alternative methods of screening cancer including visual inspection after application of 3-5% of acetic acid and Lugol's iodine. The major disadvantage of these tests is low specificity. Given the considerable variation in the way these tests are applied and interpreted in different settings, there is no standard universally accepted definition of the test results. It remains to be seen if the specificity can be improved by further developments in test definitions and training strategies.
The increase in accuracy of the cell pathology tests will substantially decrease the need for invasive biopsy. While various technical solutions can improve the cell pathology tests and decrease the ambiguity of practitioner's interpretation (see, e.g., U.S. Patent Publication No. 2004/0137551), the problems in further improvement may have fundamental restrictions. Cytological tests are based on visual identification of abnormal cells, which could, for example, be the result of inflammation or irritation. HPV DNA testing detects just HPV infection, but not the cancerous or precancerous cells. In addition, there must be a sufficient amount of infected cells to be detected with DNA tests. Thus, there is a need for a new breakthrough to increase the accuracy of the above methods of detection of cervical cancer cells, preferably at the single cell level. A combination of cell pathology tests together with the use of biomarkers (physiomarkers) specific to cervical cancer cells (at the single cell level) is likely to be the right answer. The end product, the physiomarkers of cervical cancer can then be combined with the cell pathology tests to make the combined method sensitive, accurate, fast, and minimally invasive.
Atomic force microscopy (“AFM”) method was invented in 1986 (Binnig et al. Atomic force microscope. Phys. Rev. Lett., 56, 930-933, 1986). This technique is based on detection of forces acting between a sharp probe, the AFM tip, and sample surface. The tip is attached to a very flexible cantilever. Any motion of the cantilever is detected by various methods. The most popular is an optical system of detection. Laser light is reflected from the cantilever and detected by a photodiode. The tip is brought to a contact, engaged with the surface of interest. Scanning over the surface, the AFM system records the deflection of the cantilever with sub-nanometer precision. The AFM technique has been previously used to study cells (Pelling et al., Nanoscale visualization and characterization of Myxococcus xanthus cells with atomic force microscopy. Proc Natl Acad Sci USA, 102, 6484-9, 2005; Matzke et al., Direct, high-resolution measurement of furrow stiffening during division of adherent cells. Nat Cell Biol, 3, 607-10, 2001; Suresh, Biomechanics and biophysics of cancer cells. Acta Biomater, 3, 413-38, 2007; Sokolov, Atomic Force Microscopy in Cancer Cell Research. In: WEBSTER, H. S. N. A. T. (ed.) Cancer Nanotechnology—Nanomaterials for Cancer Diagnosis and Therapy. Los Angeles: APS, 2007; Lekka et al., The effect of chitosan on stiffness and glycolytic activity of human bladder cells. Biochim Biophys Acta, 1540, 127-36, 2001; Sokolov et al., Detection of surface brush on biological cells in vitro with atomic force microscopy. Applied Physics Letters, 91, 023902-1-3, 2007), including cancerous cervical cells (Iyer et al., Towards nonspecific detection of malignant cervical cells with fluorescent silica beads. Small, 5, 2277-2284, 2009, Iyer et al., AFM Detects Differences in the Surface Brush on Normal and Cancerous Cervical Cells. Nat Nanotechnol, 4, 389-393, 2009). The recently proposed new AFM mode, HarmoniX™ (Sahin et al., An atomic force microscope tip designed to measure time-varying nanomechanical forces. Nat Nanotechnol, 2, 507-14, 2007) as well as PeakForce™ (U.S. Patent Publication No. 2010/0122385) allows not only imaging cell surfaces but also obtaining maps of surface distribution of the rigidity modulus, dissipation energy, and adhesion, etc.